Impaired induction of blood‐brain barrier properties in aortic endothelial cells by astrocytes from GFAB‐deficient mice

Cell culture models have been extensively used for studies of blood‐brain barrier (BBB) function. However, most in vitro models fail to reproduce the peculiar physiological and morphological properties of in situ brain microvascular endothelial cells. A recently developed, tridimensional and dynamic model of the BBB has permitted studies of glial‐endothelial interactions in hollow fibers exposed to intraluminal flow. We have taken advantage of this technique and have investigated the ability of glial fibrillary acidic protein (GFAP)‐deficient (GFAP −/− ) astrocytes to induce BBB properties in aortic endothelial cells (BAEC) cultured in vitro. BAEC exposed to flow were seeded intraluminally in hollow fibers and co‐cultured with extraluminally seeded mouse astrocytes. Under these conditions, astrocytes have been shown to induce blood‐brain barrier properties in non‐brain endothelial cells. We followed induction of a BBB phenotype by measuring the transendothelial resistance, as well as endothelial permeability to potassium, theophylline, 8‐sulphophenyl‐theophylline (8‐SPT), sucrose, and Evans blue. Wild‐type mouse astrocytes induced BBB properties in aortic endothelial cells following 3–4 weeks of co‐culturing. Thus, these endothelial cells restricted passage of K + ions into the extracapillary space and selectively excluded hydrophilic molecules, such as 8‐SPT and 14 C‐sucrose. GFAP −/− astrocytes failed to induce a significant restriction to the passage of potassium and hydrophilic drugs (sucrose, 8‐SPT), failed to induce transendothelial resistance values comparable to control co‐cultures, but were capable of inducing exclusion of Evans blue by endothelial cells. These results suggest that GFAP (and intermediate filaments) may play a role in the induction of BBB properties in non‐BBB endothelial cells. GLIA 22:390–400, 1998. © 1998 Wiley‐Liss, Inc.